1. Field of the Invention:
The present invention relates to a recording and/or reproducing apparatus in which, a disc-shaped record bearing medium is used.
2. Description of the Prior Art:
In the case of a recording and/or reproducing apparatus for recording and/or reproducing information with use of a record bearing medium such as a rotary magnetic disc, it is important to mount the record bearing medium on a rotation driving shaft correctly and securely in order to avoid eccentricity of the like. If the record bearing medium is not correctly mounted on the rotation driving shaft, the facing of a recording and/or reproducing head with the record bearing medium is not perfect (for example, a spacing loss increases). Or, in the case of eccentricity, a deviation occurs between the head and a track, and the recording or reproducing property becomes inferior, which is problematic.
In order to avoid the above difficulty, a method in which a pressing member is used to press the record bearing medium against a conical part which is provided on a record bearing medium rotating shaft has been proposed. However, according to this method, the record bearing medium is always pressed against the conical part of the driving shaft and the pressing member rotates together with the record bearing medium, so that the moment of inertia of the rotating portion increases and also the size of a motor for driving the rotating shaft increases, which is disadvantageous for a compact apparatus.
In order to avoid the above disadvantage, as described later, an apparatus has been proposed in which: a plastic center hub having an engaging hole for engaging with a rotating driving shaft is provided at a central portion of a flexible magnetic disc, and a spring portion for side pressure is formed on a part of the hole, so as to obtain side pressure between the driving shaft and the center hub; and at a lower part of the center hub a magnetizable plate such as one made of iron is secured, while at a flange portion of the driving shaft for determining a height of a disc relative to a recording and/or reproducing head a permanent magnet is disposed, so as to effect chucking of the disc by the magnetic attracting force between the magnetizable plate and the permanent magnet.
However, even in the case of the above method, for example, when the side pressure of the spring portion formed in the engaging hole of the center hub is low, eccentricity of the disc is apt to occur. Conversely when the side pressure is high, chucking by the attracting force between the magnetic plate of the center hub and the permanent magnet at the side of the rotating driving shaft becomes uncertain. In order to obtain a sure chucking, the permanent magnet has to be made large, which means that the load for the motor is increased, and therefore the motor as well, has to be made large, which is disadvantageous.